1. Field of the Invention
The present invention relates to a leadframe included is a resin-sealed semiconductor device.
2. Description of the Background Art
When a resin-sealed semiconductor device, for example, fabricated, a leadframe is prepared to mount a semiconductor element (chip) thereon.
FIG. 18 is a perspective view showing a configuration of a background-art leadframe 100. A metal sheet is processed to form the leadframe 100. The leadframe 100 has a pad 2 for mounting the semiconductor element 3 at its center portion, which is supported by suspension leads 6a to 6d from four directions. Inner leads 5 radially extend from the periphery towards the pad 2. The inner leads 5 are connected b electrode portions of the semiconductor element 3 with metal thin wires 4.
After the leadframe 100 in the state of FIG. 18 is obtained, the semiconductor element 3 is sealed in resin such as epoxy resin and the inner leads 5 and the suspension leads 6a to 6d are cut off from the leadframe 100.
In a case of a semiconductor package which includes a larger number of inner leads 5, such as a multiple pin QFP (Quad Flat Package), each inner lead 5 becomes narrower sad longer and its rigidity becomes lower. To prevent deformation of such inner lead 5 in a fabricating process, a support tape is applied to the inner leads 5 and the suspension leads 6a to 6d. As to the support tape, a variety of forms are proposed as below.
FIG. 18 shows a rectangular ring-shaped support tape 201. The rectangular ring-shaped support tape 201 is applied to the inner leads 5 and the suspension leads 6a to 6d around the pad 2. Since the support tape is rectangular, the inner leads 5 and the suspension leads 6a to 6d are not deformed or displaced even if the support tape 201 contracts.
FIG. 19 is a plan view illustrating a manner of taking the support tape 201 out of its material. The material 200 for the support tape 201 is generally supplied in tape form, and a rectangular ring-shaped support tape 201 is punched and applied to the inner leads 5. In this case, there are remaining portions 202 and 203, and the material 200 is disadvantageously utilized with low efficiency. In general, the material 200 is expensive, and therefore inefficient use of the material 200 leads to a costly leadframe 100.
To solve the problem of the structure of FIG. 18, use of strip shaped support tapes, instead of rectangular ring-shaped support tapes, is proposed. FIG. 20A is a plan view showing a configuration of a leadframe 101 and FIG. 20B is a section taken along the line 20Bxe2x80x9420B and viewed from the direction of the arrow of FIG. 20A.
The support tapes 211 and 221 are of strip-shape and applied to all of the inner leads and suspension leads 6a to 6d. FIG. 21 is a plan view illustrating a manner of taking the support tapes 211 and 221 out of their materials 210 and 220 in tape form. The support tapes 211 and 221 can be taken out of the materials 210 and 220 with higher efficiency than in the structure of FIG. 18 since those support tapes are rectangular.
With this type of support tapes, however, the inner leads 5 are deformed at the suspension leads 6a to 6d and their vicinities, e.g., in an area A including the suspension lead 66 and its vicinity. FIG. 22 is as enlarged plan view of an area A and its vicinity of FIG. 20A. Among the inner leads 5, an inner lead 501 adjacent to the suspension lead 6b to which both the support tapes 211 and 221 are applied is pulled in the directions of the arrows by contractions of the support tapes 211 and 221. The inner lead 501 is thereby deformed and comes into contact with an adjacent inner lead 502 at a point B. Then, the suspension lead 6b and the inner lead 502 are also deformed.
To solve the problems of the structure of FIGS. 18 and 20A, it is also proposed that the strip-shaped support tapes 211 and 221 should be applied to the inner leads 5 and the suspension leads 6a to 6d with their end portions over-lapped. FIG. 23A is plan view showing a configuration of a leadframe 102 and FIG. 23B is a section taken along the line 23Bxe2x80x9423B of FIG. 23A and viewed from the direction of the arrow.
The end portions of the strip-shaped support tapes 211 and 221 are overlapped to form a rectangular ring-shaped support tape on the whole and further their materials 210 and 220 can be utilized with higher efficiency. Moreover, at their overlapped end portions, stresses generated by contraction along the directions of the respective lengths of the support tapes 211 and 221 are balanced and the suspension leads 6a to 6d are given stresses only in a direction towards the pad 2. That avoids deformation of the suspension leads 6a to 6b.
It is not desirable, however, that many portions are each given stresses in different directions at an angle of 90xc2x0 when the support tapes contract. The reason is the alignment of their end portions to be overlapped should be accurately made in order to balance the stresses applied to the support tapes 211 and 221 along the directions of their lengths.
The present invention is directed to a leadframe. According to a first aspect of the present invention, the leadframe comprises: a plurality of inner leads provided radially; and a group of support tapes applied to the plurality of inner leads in a ring shape, in which inner end portions of the plurality of inner leads expose on inner peripheral side of the group of support tapes, and in which the group of support tapes includes a plurality of first support tapes of L-shape, and both and portions of one of the plurality of first support tapes are overlapped with end portions of at least one of the plurality of first support tapes which is different from said one of the plurality of first support tapes.
According to a second aspect of the present invention, in the leadframe of the first aspect, the group of support tapes includes two first support tapes.
According to a third aspect of the present invention, the leadframe of the fast aspect further comprises: a pad of substantially rectangular surrounded by the plurality of inner leads, in which the respective center portions of the plurality of first support tapes are located on two opposed ones of four suspension leads which are inner leads for supporting the pad at its four corners.
According to a fourth aspect of the present invention, in the leadframe of the third aspect, one of the plurality of first support tapes is applied to a front surface of the inner leads and the other is applied to a back surface of the inner leads, and the respective end portions are overlapped with each other through the inner leads.
According to a fifth aspect of the present invention, in the leadframe of the second aspect, each of the end portions of the plurality of first support tapes has a chipped portion having an angle of almost 45xc2x0 in its extending direction.
According to a sixth aspect of the present invention, in the leadframe of the first aspect, the group of support tapes includes four first support tapes.
According to a seventh aspect of the present invention, the leadframe of the sixth aspect further comprises: a pad of substantially rectangular surrounded by the plurality of inner leads, in which the respective center portions of the plurality of first support tapes are located on four suspension leads which are inner leads for supporting the pad at its four corners.
According to an eighth aspect of the present invention, in the leadframe of the seventh aspect, a first pair of the plurality of first support tapes are opposed to each other and a second pair of the plurality of first support tapes are opposed to each other, the first pair and the second pair are different from each other, the first pair is applied to a front surface of the inner leads and the second pair is applied to a back surface of the inner leads, and end portions of the first support tapes are overlapped with adjacent ones through the inner leads.
According to a ninth aspect of the present invention, the leadframe comprises: a plurality of inner leads provided radially; and a group of support tapes applied to the plurality of inner leads in a ring shape, in which inner end portions of the plurality of inner leads expose on inner peripheral side of the group of support tapes; and in which the group of support tapes includes a plurality of first support tapes of L-shape and a plurality of second support tapes of strip-shape, and both end portions of one of the plurality of first support tapes are overlapped with end portions of the plurality of second support tapes.
According to a tenth aspect of the present invention, in the leadframe of the ninth aspect, the plurality of first support tapes are applied to a front surface of the inner leads and the plurality of second support tapes are applied to a back surface of the inner leads, and end portions of the first support tapes are overlapped with end potions of second support tapes through the inner leads.
The leadframe of the first aspect employs L-shaped fast support tapers, and therefore achieves higher efficiency in utilizing the material for support which is generally in tape form.
When the support tapes are overlapped in a portion where stresses may be generated in different directions at an angle of 90xc2x0, the overlapping should be made with sufficient accuracy. The leadframe of the second and third aspects needs only two overlapped portions of the support tapes, and therefore the number of then overlapped portions requiring sufficient accuracy in overlapping is reduced.
The leadframe of the fifth aspect employs the first support tapes with end portions each having a chipped portion at an angle of almost 45xc2x0, and therefore makes it possible to take the first support tape having longer sides out of the material for support tape. That allows standardization of width of the material for support tape for a variety of leadframes of different sizes, and thereby facilitates an abundant supply of materials for support tapes of few kinds, resulting in a lower price of the material for support tape.
Although the leadframe of the sixth and seventh aspects needs four overlapped potions of the support tapes, no stress in different directions at an angle of 90xc2x0 is generated at the overlapped portions. Therefore, the leadframe has no overlapped portion requiring sufficient accuracy in overlapping.
The second support tapes used in the leadframe of the ninth aspect are of strip-shape, and therefore can be taken oat of the material for support tape with much higher efficiency. Moreover, since the second support tape is interposed between the first support tapes, it is possible to standardize width of the material for support tape for a variety of leadframes of different sizes, even for a larger leadframe regardless of the extent of the enlargement. That facilitates an abundant supply of materials for support tapes of few kinds, resulting in a lower price of the material for support tape.
The leadframe of the fourth, eighth and tenth aspects has no overlapped portion of any two support tapes on its front surface, and therefore suppresses degradation of accuracy in resin-sealing.
An object of the present invention is to reduce the number of overlapped portions of the support tapes where the stresses are generated in different directions at an angle of 90xc2x0, for reduction in the number of portions requiring accurate alignment in overlapping, and further to suppress deformation of an inner lead at a low cost by using the support tape which can be taken out of the material with higher efficiency.
These and other objects features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken is conjunction with the accompanying drawings.